1. Field of the Invention
The present invention relates to the electrostatic separation of kieserite (MgSO4.H2O) from crude potassium salts, which contain not only kieserite but also other minerals such as sylvin, halite, polyhalite, langbeinite, and other salt minerals.
2. The Prior Art
It is known to isolate the mineral kieserite from crude salts of potassium beds using a dry electrostatic separation method (G. Fricke, “Die elektrostatische Aufbereitung von Kalium—und Magnesiumsalzen” [Electrostatic treatment of potassium and magnesium salts], Kali und Steinsalz [Potassium and Mineral Salt], Issue 9/1986, p. 278-295). For this purpose, the crude salt is ground, classified to a predetermined grain size, provided with a small amount of conditioning agent, usually of an organic type, and swirled up with air having a specified temperature and moisture content, triboelectrically charged, and the mixture is separated into a crude kieserite fraction and a crude potassium fraction in an electrostatic field.
German Patent No. DE 1 667 814 describes such a separation method for obtaining the mineral kieserite, in a first step, from a crude potassium salt containing kieserite, using aliphatic, unbranched fatty acids having a chain length C3 to C18, or aromatic carboxylic acids, or a mixture of the two aforementioned, as well as ammonium salts of the low aliphatic fatty acids, preferably ammonium formiate and ammonium acetate, as conditioning agents, at a relative humidity of 5% to 40%, preferably 10% to 30%.
In German Patent No. DE 4 039 470 C1, a conditioning agent formulation is listed that is composed of the substances salicylic acid, fatty acid, and ammonium acetate. According to the method described, air having a relative humidity of 5% is used for conditioning.
In the case of this formulation, however, it has been shown in practice that the substances used here bring about problems in a flotative treatment of the crude potassium fraction that follows the electrostatic treatment. Thus, the fatty acid used can lead to unselective hydrophobization of all of the mineral phases in flotation. Also, there are handling difficulties due to the hygroscopic properties of ammonium acetate. It was also shown that under these conditions, as much as about 20% of the kieserite contained in the crude salt cannot be separated into the crude kieserite fraction, but rather is lost in the crude potassium fraction.